Mass storage units are commonly used in applications where large amounts of data need to be stored. Typically, such mass storage units each contain a number of disk drives connected via a bus, such as a differential Small Computer System Interface (SCSI) bus that is standard in the art. Such mass storage units typically include one or more bus controller cards to control the bus. Those one or more cards generally connect to a backplane on which the bus is implemented.
The bus controller card or cards may include high-voltage differential (HVD) transceivers. HVD transceivers are adapted for use with a differential SCSI bus carrying HVD signals at +5V, as defined in the SCSI-2 standard. A differential SCSI bus typically carries a diffsense signal that is used to characterize the bus. The voltage of the diffsense signal is associated with the type of SCSI bus in use. A diffsense voltage between 0 and 0.5 V is associated with a single-ended bus; a diffsense voltage between 0.7 and 1.9 V is associated with a low-voltage differential (LVD) bus; and a diffsense voltage of 2.4 V or greater is associated with an HVD bus. The diffsense signal is used to sense the type of bus signals utilized, and to switch devices connected to the bus on or off depending on the type of bus signals. Thus, those devices are protected from bus signals with which they are incompatible. However, sensing and acting on the diffsense signal alone do not protect the devices connected to the SCSI bus from other hazards.